Dual-lumen catheters have been available for many years for a variety of medical purposes. It is only in recent years, however, that such catheters have been developed for use in hemodialysis and other treatments which involve the removal and replacement of blood. The general form of dual-lumen catheters goes back to as early as 1882 when Pfarre patented such a catheter in the United States under Ser. No. 256,590. This patent teaches a flexible dual-lumen catheter which is used primarily for cleaning and drainage of, for example, the bladder, rectum, stomach and ear. In this type of catherization, the catheter is introduced into an existing body orifice without the use of any puncturing needle or guide wire.
More recently, a catheter was developed and patented by Blake et al. under U.S. Pat. No. 3,634,924. This patent teaches a double lumen cardiac balloon catheter which is introduced into a large vein and the balloon is inflated to control the flow in the vein. The catheter can be placed by using the balloon as a “sail” to move with the blood from an ante-cubital or other peripheral vein through for example, the right heart chambers into the smaller radicals of the pulmonary artery where the catheter takes up its intended function. This patent teaches the use of two lumina in a single body and explains how to make a tip for a dual-lumen structure of the type which has become common for a variety of purposes including hemodialysis. The structure uses a plug to seal the end of one lumen and a wire which retains the shape of the other lumen during formation of the tip in a heated die.
Further patents which teach dual-lumen or multiple lumen catheters for general use include the following: U.S. Pat. Nos. 701,075; 2,175,726; 2,819,718; 4,072,146; 4,098,275; 4,134,402; 4,180,068; 4,406,656; 4,451,252; 5,221,255; 5,380,276; 5,395,316; 5,403,291; 5,405,341; 6,001,079; 6,190,349; 6,719,749; 6,758,836; and 6,786,884, the disclosures of each of which are incorporated herein in their entirety.
Vascular catheter access techniques have been known to the medical profession for many years and, in fact, can be traced back to the 17th century. However, it was only with the introduction of the Seldinger technique in the early 1950s that a new approach could be used to improve vascular access. This technique was taught in an article published by Dr. Sven Ivar Seldinger resulting from a presentation made at the Congress of the Northern Association of Medical Radiology at Helsinki in June of 1952. The technique essentially involves the use of a hollow needle to make an initial puncture, and a wire is then entered through the needle and positioned in the vessel. The needle is withdrawn and the catheter is entered percutaneously over the wire which is itself later withdrawn. With this technique it became possible to make less traumatic vascular access and this has now become the accepted method of performing access in numerous medical techniques. One of these techniques which been the subject of much research and development is hemodialysis.
Hemodialysis can be defined as the temporary removal of blood from a patient for the purpose of extracting or separating toxins therefrom and the return of the cleansed blood to the same patient. Hemodialysis is indicated in patients where renal impairment or failure exists, that is, in cases where the blood is not being properly or sufficiently cleansed, particularly to remove waste materials and water, by the kidneys.
In the case of chronic renal impairment or failure, hemodialysis has to be carried out on a repetitive basis. For example, in end-stage kidney disease where transplantation of kidneys is not possible or for medical reasons is contra-indicated, the patient may have to be dialyzed about 100 to 150 times per year. This can result in several thousand accesses to the blood stream to enable hemodialysis to be performed over the remaining life of the patient.
Towards the end of 1960, Dr. Stanley Shaldon and colleagues developed, in the Royal Free Hospital in London, England, a technique for hemodialysis by percutaneous catheterization of deep blood vessels, specifically the femoral artery and vein. The technique was described in an article published by Dr. Shaldon and his associates in the Oct. 14, 1961 edition of The Lancet at Pages 857 to 859. Dr. Shaldon and his associates developed single lumen catheters having tapered tips for entry over a Seldinger wire to be used in hemodialysis. Subsequently, Dr. Shaldon and his colleagues began to insert single lumen inlet and outlet catheters in the femoral vein and this was reported in the British Medical Journal of Jun. 19, 1963. The purpose of providing both inlet and outlet catheters in the femoral vein was to explore the possibility of a “self-service” approach to dialysis. Dr. Shaldon was subsequently successful in doing this and patients were able to operate reasonably normally while carrying implanted catheters which could be connected to hemodialysis equipment periodically.
An advantage of dual-lumen catheters in hemodialysis is that only one vein access need be affected to establish continued dialysis of the blood. One lumen serves as the conduit for blood flowing from the patient to the dialysis unit and the other lumen serves as a conduit for treated blood returning from the dialysis unit to the patient. This contrasts with prior systems where either two insertions were necessary to place two separate catheters as was done by Dr. Shaldon, or a single cathether was used with a complicated dialysis machine which alternately removed blood and returned cleansed blood.
The success of Dr. Shaldon in placing catheters which will remain in place for periodic hemodialysis caused further work to be done with different sites. Dr. Shaldon used the femoral vein, and in about 1977 Dr. P. R. Uldall, in Toronto Western Hospital, Canada, began clinical testing of a subclavian catheter that would remain in place between dialysis treatments. An article describing this was published by Dr. Uldall and others in Dialysis and Transplantation, Volume 8, No. 10, in October 1979. Subsequently Dr. Uldall began experimenting with a coaxial dual-lumen catheter for subclavian insertion and this resulted in Canadian Patent No. 1,092,927 which issued on Jan. 6, 1981. Although this particular form of catheter has not achieved significant success in the marketplace, it was the forerunner of dual-lumen catheters implanted in the subclavian vein for periodic hemodialysis.
The next significant step in the development of a dual-lumen catheter for hemodialysis is Canadian Patent No. 1,150,122 to Martin. A subsequent development is shown in U.S. Pat. No. 4,451,252 also to Martin. This catheter utilizes the well-known dual-lumen configuration in which the lumina are arranged side-by-side separated by a diametric septum. The structure shown in this patent provides for a tip making it possible to enter a Seldinger wire through one of the lumina and to use this wire as a guide for inserting the catheter percutaneously. This type of structure is shown in a European Patent Application to Edelman published under No. 0 079 719, and in U.S. Pat. Nos. 4,619,643; 4,583,968; 4,568,329; 4,543,087; 4,692,141; 4,568,329, and U.S. Des. Pat. No. 272,651, the disclosures of each of which are incorporated herein in their entirety.
In order to insert a catheter over a guide wire using the Seldinger technique, or indeed any similar technique, the tip of the catheter must possess sufficient rigidity so that it does not concertina as it contacts the skin because this would enlarge the skin puncture as the catheter is being entered over the wire. To some extent this is at odds with the desirable material qualities of the main body of catheter which should be soft and flexible for patient comfort. In an effort to solve this problem, a variety of tips have been formed within the limitations of using a single extrusion from which the body and tip are formed. The result is that the tips have in general been made by using some of the excess material found in the shorter intake lumen. This has led to other problems such as very stiff tips which are unsuitable for prolonged placement in a vein; voids which can accumulate stagnant blood; and short stubby tips which are less desirable for insertion than longer more gradual tips. Also, because there is not always sufficient material to form the tip, plugs have been added with a varying degree of success because if the plug is not placed accurately the resulting structure may have unacceptable spaces where blood can stagnate.
It must also be recognized that the degree of rigidity in the tip becomes more important if the catheter is to reside in the patient for prolonged periods, as is becoming more common in many treatments, notably hemodialysis. This is because although ideally the catheter lies in the middle of the vein, in practice it will often bear against the vessel wall. In such circumstances it is possible that a stiff tip could damage or even embed itself in the vessel wall when left in place for extended periods.
Hemodialysis, as practiced today, normally employs one of two types of catheters to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a dual-lumen catheter is used, each lumen having either a generally cylindrical or semi-cylindrical configuration. Alternatively, two separate tubes, each usually having a full cylindrical configuration, are used separately to remove blood for dialysis and return the processed blood.
Flow rates possible with conventional dual-lumen catheters are usually lower than those achievable where separate tubes are used to remove blood from a vein for dialysis and then return processed blood back to the vein. Thus, the use of two tubes has become more and more popular as the capacity (maximum flow rate) of hemodialysis membranes has increased.
Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein and the line removing blood for purification at flow rates above 300 ml per minute. A high flow rate from the venous line may cause whipping or “firehosing” of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line may cause the port to be sucked into the vein wall, resulting in occlusion.
The rate of flow through a catheter lumen, whether it be in a single lumen or a dual-lumen catheter, is controlled by a number of factors including the smoothness of the wall surface, the internal diameter or cross-sectional area of the tube lumen, and the length of the tube lumen. The most important factor is the cross-sectional area of the tube lumen. The force or speed of the fluid flow in a tube lumen for a given cross-sectional area is controlled by the external pumping force. This is a positive pressure pushing processed blood through the venous lumen and a negative (suction) pressure pulling unprocessed blood through the arterial lumen.
Problems encountered in providing for a high flow rate through a catheter are magnified in a dual-lumen catheter construction. Because each of the lumina in a dual-lumen catheter normally has a D-shape, it has been assumed that flow rates are limited. Furthermore, such dual-lumen catheters are, to a great extent, catheters with a main port which opens at the end of a lumen substantially on the axis of the lumen. Thus, firehosing frequently results. Firehosing may damage the vein wall, triggering the build-up of fibrin on the catheter tip. Fibrin build-up may further result in port occlusion.
There are dual lumen-catheters which utilize side ports for both outflow and inflow. An example is the catheter disclosed in U.S. Pat. No. 5,571,093 to Cruz et al. However, such catheters have not been entirely successful in solving problems related to hemodialysis with dual lumen catheters, e.g., high incidences of catheter port occlusion as well as some degree of fire-hosing. Further, the abrupt change in direction of the flow of blood from the vein into the catheter can result in trauma and damage to red blood cells, especially at higher flow rates.